<!DOCTYPE html>
<heml>
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

    <title>第一个</title>
    <style type="text/css">
    .header{
        background-color:rgb(224, 28, 28);
        height: 30px;
  
    }
    </style>
    </head>
    <body>
     <div class="header"></div>

        
    </body>
</heml>